1. Field of the Invention
This invention relates to a process for the preparation of 2-(methylthiomethyl)-6-(trifluoromethyl) aniline [MTA] from ortho-aminobenzotrifluoride [OABT].
2. Description of the Prior Art
The preparation of ortho-(methylthiomethyl) anilines from the corresponding anilines via sulfilimine intermediates is known. Claus, Tetrahedron Letters, p. 3607 (1968), describes the preparation of aromatic sulfilimines from anilines and dimethylsulfoxide in the presence of P.sub.2 O.sub.5 in a base such as triethylamine. Claus also discloses thermal rearrangement of these sulfilimines to ortho-(methylthiomethyl) anilines. See also, Gassman, Tetrahedron Letters, p. 497 (1972) and Johnson, Tetrahedron Letters, p. 501 (1972). Gassman discloses the use of N-t-butyl anilines to generate N-t-butyl-N-chloro anilines, generally employing an alkyl-hypochlorite and subsequently sulfilimine salts with dimethyl sulfide which, upon treatment with a base under anhydrous conditions, were converted to N-substituted ortho-(methylthiomethyl) anilines. Vilsmaier, Tetrahedron Letters, p. 625 (1972) describes the reaction of anilines with dimethyl sulfide and N-chlorosuccinimide to form sulfilimine hydrochloride salts. Vilsmaier here does not teach the rearrangement of the sulfilimine or its salt. Another method of preparation of sulfilimine salts is disclosed in Claus and Vilsmaier, Tetrahedron Letters 31, p. 505 (1975). This article, like the previous Vilsmaier article, discloses the reaction of anilines with dimethyl sulfide in the presence of N-chlorosuccinimide to form the sulfilimine hydrochloride salt. In the Claus and Vilsmaier reference the sulfilimine hydrochloride salt is neutralized with aqueous caustic but Claus and Vilsmaier do not disclose the rearrangement of the sulfilimine produced by this process. See also Gassman U.S. Pat. Nos. 3,894,034, 3,954,797, 3,960,926, 3,985,756 and 4,035,375. The Gassman patents generally relate to the preparation and essentially anhydrous rearrangement of sulfilimine salts to produce ortho-(methylthiomethyl) anilines. Claus, et al., Phosphorus and Sulfur, 1, pp. 11, 18 (1976) (and references cited therein) and U.S. Pat. No. 4,172,095 describe sulfilimine rearrangement in the presence of alchohols such as ethanol or t-butanol.
The prior art processes for preparing ortho-(methylthiomethyl) anilines via the sulfilimine route generally exhibit a number of drawbacks which make them undesirable for commercial scale conversion processes. These prior art sulfilimine formation and rearrangement reactions proceed satisfactorily at the laboratory scale but they employ reagents which are expensive, often dangerous, and difficult to work with on a larger scale. One of the most serious of these drawbacks is the generally held requirement for processing under anhydrous conditions and utilizing dry organic bases such as tertiary amines. Moreover, the rearrangement of sulfilimines to ortho-(methylthiomethyl) anilines was thought to require high temperatures, the presence of alchohols or dry basic catalysts such as triethylamine.
Accordingly it is an object of the present invention to provide a process for the smooth and efficient conversion of ortho-aminobenzotrifluoride to MTA which substantially avoids the drawbacks of the prior art.
More specifically, it is an object of the present invention to provide a process for the conversion of OABT to MTA in which the overall conversion process is carried out in a single common organic solvent.
It is another object of the present invention to provide a process for the conversion of OABT to MTA in which inexpensive aqueous caustic solution is utilized to neutralize the sulfilimine hydrochloride salt formed and to extract at least a major portion of succinimide formed.
It is also an object of the present invention to provide a process for converting OABT to MTA having improved economies by virtue of conversion of aqueous succinimide by-products to N-chlorosuccinimide for recycle to the sulfilimine hydrochloride salt preparation step.
It is a further object of this invention to provide a process for the conversion of OABT to the MTA in which no alcohols or dry organic bases are utilized in either neutralization of the sulfilimine hydrochloride salt or its rearrangement.
It is another object of this invention to include only a minor (catalytic) amount of succinimide when rearranging the neutral sulfilimine.